1. Field of the Invention
The present invention relates to an image pick-up apparatus, a control method thereof, and a computer readable memory medium, and more particularly to an image pick-up apparatus having a multi-area AF function, a control method thereof, and a computer readable memory medium.
2. Description of the Related Art
Recently, digital cameras with a multi-area AF (Auto-Focus) function have become available.
With the multi-area AF function is for executing an AF process, plural AF areas are prepared, and one area is automatically selected from among the plural AF areas as an area in which the subject of the imaging is to be automatically focused on. For example, an AF area where a subject is closest to a user's location may be selected for the AF process.
In addition, digital cameras are available which are provided with an AE (Automatic Exposure) processing function, which measures the intensity of light to determine an appropriate exposure, and which automatically sets an appropriate aperture and shutter speed based on the determined exposure. Various techniques for measuring the intensity of light falling on a subject are used, such as an “average metering system”, a “center-weighted metering system” and a “spot metering system”. The “average metering system” is a photometry system used to measure the intensity of light falling on the entire are of an image. The “center-weighted metering system” is a photometry system used to measure the intensity of light falling on the middle portion of image data. That is, in the “center-weighted metering system”, the metering area is set throughout the whole image, and more weight is given to image data in the vicinity of the middle of the image and less weight is given to image data in the other areas of the image when calculating the appropriate exposure. The “spot metering system” is a photometry system used to measure the intensity of light falling on a specific portion of image data.
In conventional techniques, there is no correlation between the AE process and the AF process. To solve a problem whereby the AE process and the AF process are executed respectively on different portions of a subject, a technique has been proposed in which the AE process and AF process are executed on areas of the subject coupled with each other (JP Hei8-9236 JP).
This technique, however, causes another problem. For example, in the case where the “multi-area AF system” is set, even if the user selects the “center-weighted metering system” because a subject (e.g., a girl shown in FIGS. 9A and 9B) to be photographed is located in the vicinity of the middle of an image as shown in FIG. 9A, a problem can be caused that another AF area (e.g., the stippled area in FIG. 9B) is focused on instead of an AF area in which the subject appears. In FIGS. 9A and 9B, numeral 21 denotes a metering area, 22 denotes a center-weighted area, and 23 denotes AF areas. In the “center-weighted metering system”, the metering area 21 is set throughout the whole image, and the center-weighted area 22 indicates an area of the image which is located in the vicinity of the middle of the image, and which is given more weight. The technique disclosed by JP Hei8-9236 A cannot solve the problem caused when the “multi-area AF system” is set.